Which of the following is key to maintaining healthy nails?

Regular moisturizing is crucial for maintaining healthy nails. Moisturizing helps keep the nails and the surrounding skin hydrated, which is essential for preventing dryness, brittleness, and potential breakage. Moisturizers contain ingredients that can enhance the overall appearance of the nails, making them look healthier and stronger.

Hydrated nails are less prone to cracking and splitting, which can lead to more serious nail issues. Moisturizing also benefits the cuticles, which protect the nail matrix, the area where new nail growth occurs. When cuticles are well-moisturized, they maintain their resilience and elasticity, supporting overall nail health.

The other choices involve practices that can be harmful if performed to excess or without proper care. Frequent filing may lead to weakening of the nail, while constant polishing can hinder the nails' natural ability to breathe and may also introduce harmful chemicals. Excessive buffing can thin the nail plate, making it more susceptible to damage. Therefore, regular moisturizing stands out as the most beneficial practice for healthy nails.